Air quality in Redding could improve in the next few days. Here's why.

In the northeast section by Bollibokka Club along McCloud River on Saturday, Aug. 18, 2018 a helicopter drops water on a hot spot on the ridge. Helicopters have been collecting water from Lake Shasta at Hirz Bay area to drop on the fire. (Special to the Record Searchlight/Hung T. Vu)(Photo: Hung T. Vu)Buy Photo

Buoyed by south winds, smoke from the Hirz Fire burning north of Lake Shasta — and to a lesser extent, other wildfires in the region — was pushed out of here, bringing in blue skies and improving air quality.

But over the Labor Day weekend, the winds relaxed a bit and shifted to the north, allowing those smoky skies to return. Monday and Tuesday also brought smoke intermittently into the Redding area.

But relief could be on the way: the National Weather Service is forecasting more wind from the south through Thursday.

"A lot of it depends on what type of operations are going on with the Hirz Fire since that fire is proving most impactful to the northern Sacramento Valley,” said John Waldrop, Shasta County's air quality district manager.

Over the weekend, firefighters were conducting back-burning operations to help secure containment lines around the fire. That, combined with the winds slowing and shifting north, contributed to the smoky skies.

The Hirz Fire was 60 percent contained and had burned more than 46,000 acres, the U.S. Forest Service said Tuesday.

The air quality index in Shasta County was at unhealthy levels as of noon Tuesday, which means everyone may experience health effects from the smoke in the air.

Airnow.gov, the official Environmental Protection Agency website that measures the index, is a 24-hour average, Waldrop said.

Another popular air quality site is Purpleair.com, which gives real-time readings using sensors around the region, Waldrop said. It gives a new reading every 80 seconds.

Waldrop said when the air is deemed unhealthy for sensitive groups, Purple Air readings “tend to read a little on the higher side.” Also, Purple Air uses a laser beam that goes across the area to measure air quality.

The EPA monitors use filters.

Craig Shoemaker, a meteorologist with the National Weather Service in Sacramento, said cooler temperatures in the morning also push the smoke down from the Hirz Fire and into the valley.

“It’s because the cool air tends to sink, so it wants to sink down that valley,” Shoemaker said. “Cooler air goes to the lowest elevation, the lowest spot, so it gradually drains and moves down that valley during the nighttime hours and into the morning.”

But Shoemaker expects winds from the south to kick up through Thursday before they shift north Friday, which means more smoke.

And for the weekend?

“If this trough materializes, it will tend to bring more southerly winds and keep the air a little cleaner,” Shoemaker said.

The smoke has at times limited outdoor activities at schools and made it challenging for events like the annual Sunset Through the Trees, a seven week fun-run series at various locations around Redding. The runs are Tuesdays from late July to early September.

They typically draw 125 to 150 participants each week, but this year the biggest one had 55 runners, organizer John Luaces said.

"I am kind of letting runners decide, and they have decided for the most part not to show up," Luaces said.

Luaces also organizers a winter series called Frosty Fun Runs that go from early January to late February.